UPSC CSE Prelims
Satellites and Their Applications Previous Year Questions (PYQs)

Detailed Explanation:

Answer: Option 4 — Japan

Japan operates the QZSS (Quasi-Zenith Satellite System), which is a regional satellite navigation system designed to enhance GPS coverage and accuracy in the Asia-Oceania region, particularly over Japan. Among the given options, only Japan has its own satellite navigation system.

📝 Short Notes: Satellite Navigation Systems Worldwide

• Global Navigation Satellite Systems (GNSS): Four operational systems - GPS (USA), GLONASS (Russia), Galileo (European Union), and BeiDou (China) - provide worldwide coverage.
• Regional Navigation Satellite Systems: NavIC/IRNSS (India) covers Indian subcontinent and surrounding region up to 1,500 km; QZSS (Japan) enhances GPS signals in Asia-Oceania region.
• GPS (USA): First operational GNSS with 24+ satellites, launched in 1978, fully operational since 1995.
• GLONASS (Russia): Developed during Soviet era, fully operational since 2011 with 24+ satellites.
• Galileo (EU): European system providing high-precision positioning, became operational in 2016.
• BeiDou (China): Completed global coverage in 2020 with 35 satellites, serves both regional and global users.
• NavIC (India): Indian Regional Navigation Satellite System with 7 satellites, operational since 2018, provides positioning accuracy better than 20 meters.
• QZSS (Japan): Quasi-Zenith Satellite System with satellites in quasi-zenith orbits, providing enhanced positioning over Japan and neighboring regions.

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

Remote sensing technology uses satellite images to detect and monitor physical characteristics of areas by measuring reflected and emitted radiation. All three parameters mentioned can be effectively measured or estimated using satellite-based remote sensing data.

✅ Statement 1 – Correct: Chlorophyll content in vegetation is estimated by measuring light reflectance, as chlorophyll absorbs specific wavelengths for photosynthesis and the reflected light indicates chlorophyll concentration.

✅ Statement 2 – Correct: Greenhouse gas emissions from rice paddies can be estimated by detecting radiations emitted by methane and other gases, combined with thermal and spectral signatures of waterlogged conditions.

✅ Statement 3 – Correct: Land surface temperatures are directly measured by satellite sensors that detect infrared radiation emitted by the Earth's surface.

📝 Short Notes: Remote Sensing Applications

• Remote Sensing: The science of obtaining information about objects or areas from a distance, typically using satellites or aircraft-mounted sensors.
• Spectral Reflectance: Different surfaces and materials reflect electromagnetic radiation differently; vegetation reflects strongly in near-infrared while absorbing visible light for photosynthesis.
• Thermal Infrared Sensing: Used to measure land surface temperature by detecting heat radiation emitted from the Earth's surface.
• Agricultural Monitoring: Remote sensing helps monitor crop health, soil moisture, irrigation needs, and greenhouse gas emissions from agricultural activities.
• Vegetation Indices: NDVI (Normalized Difference Vegetation Index) and other indices derived from satellite data help assess vegetation vigor and chlorophyll content.
• Methane Detection: Advanced satellite sensors can detect methane emissions from rice paddies, wetlands, and other sources by measuring specific absorption bands in the infrared spectrum.

Detailed Explanation:

Answer: Option 1 — 1 only

IRNSS (Indian Regional Navigation Satellite System), also known as NavIC (Navigation with Indian Constellation), is India's independent regional navigation satellite system. Among the three statements, only the first statement correctly describes the satellite configuration of IRNSS.

✅ Statement 1 – Correct: IRNSS has three satellites in geostationary orbits (positioned at fixed points above the equator) and four satellites in geosynchronous orbits (inclined geosynchronous orbits at approximately 29° inclination).

❌ Statement 2 – Incorrect: IRNSS covers the entire India and extends approximately 1500 km beyond its borders (primary service area), not 5500 sq. km. The extended service area covers a much larger region from 30°S to 50°N latitude and 30°E to 130°E longitude.

❌ Statement 3 – Incorrect: IRNSS/NavIC is a regional navigation system, not a global navigation system. It provides coverage over India and surrounding regions only. India does not have a satellite navigation system with full global coverage as of 2019 or currently.

📝 Short Notes: IRNSS/NavIC

• Full Form: Indian Regional Navigation Satellite System (IRNSS), operational name NavIC (Navigation with Indian Constellation)
• Constellation: 7 satellites total - 3 in Geostationary Orbit (GEO) and 4 in Geosynchronous Orbit (GSO)
• Primary Service Area: India and region extending up to 1500 km from its boundary
• Extended Service Area: Region between 30°S to 50°N latitude and 30°E to 130°E longitude
• Operational Since: 2018 (all 7 satellites became operational)
• Applications: Terrestrial, aerial and marine navigation, disaster management, vehicle tracking, fleet management, integration with mobile phones, precise timing, mapping and geodetic data capture
• Administered by: Indian Space Research Organisation (ISRO)
• Ground Segment: IRNSS Spacecraft Control Facility (IRSCF) at Hassan and Bhopal, IRNSS Range and Integrity Monitoring Stations (IRIMS) at multiple locations, and Navigation Control Centres

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

GPS (Global Positioning System) is a satellite-based navigation system that provides precise geolocation and time information, making it useful across diverse applications beyond just navigation.

✅ Statement 1 – Correct: GPS is integral to mobile phone operations for location tracking, navigation apps, and location-based services like ride-hailing and food delivery.
✅ Statement 2 – Correct: GPS provides precise time-stamping for banking transactions, ensuring accurate record-keeping and synchronization across banking networks, and enables ATM location services.
✅ Statement 3 – Correct: GPS is crucial for synchronizing power grid operations by providing accurate time stamps for measurements, which is essential for grid stability and preventing blackouts.

📝 Short Notes: GPS Technology Applications

• GPS (Global Positioning System): A satellite-based navigation system owned by the US government, consisting of 24+ satellites orbiting Earth.
• Primary Function: Provides geolocation (latitude, longitude, altitude) and precise time information to GPS receivers anywhere on Earth.
• Timing Applications: GPS satellites carry atomic clocks that provide nanosecond-level time accuracy, critical for telecommunications, banking, power grids, and stock markets.
• Navigation Uses: Aviation, maritime, vehicle navigation, surveying, mapping, and military operations.
• Location-Based Services: Mobile apps, emergency services (911/112), asset tracking, agriculture (precision farming), and weather forecasting.
• Other Global Systems: GLONASS (Russia), Galileo (EU), BeiDou (China), and NavIC/IRNSS (India's regional system).

Detailed Explanation:

Answer: Option 2 — To detect gravitational waves

The evolved Laser Interferometer Space Antenna (eLISA), now known as LISA (Laser Interferometer Space Antenna), is a space-based gravitational wave observatory designed to detect low-frequency gravitational waves from cosmic sources. It uses laser interferometry to measure tiny distortions in spacetime caused by passing gravitational waves from events such as merging supermassive black holes, extreme mass ratio inspirals, and galactic binary systems. This ESA-led mission (with NASA contribution) operates in the millihertz frequency range, complementing ground-based detectors like LIGO that observe higher frequencies. The detection of gravitational waves opens a new window to observe the universe and test Einstein's general relativity in extreme conditions.

Detailed Explanation:

✅ Statement 1 – Correct: IRS satellites use multispectral and hyperspectral imaging to monitor crop health, growth patterns, and productivity assessment through vegetation indices like NDVI.

✅ Statement 2 – Correct: Remote sensing data from IRS helps identify groundwater potential zones by analyzing geological structures, lineaments, and soil moisture patterns.

✅ Statement 3 – Correct: IRS satellites provide spectral signatures of surface minerals, aiding in mineral exploration and geological mapping through techniques like lithological discrimination.

❌ Statement 4 – Incorrect: Telecommunications require geostationary communication satellites (INSAT/GSAT series), not IRS (earth observation) satellites which are designed for remote sensing, not signal relay.

❌ Statement 5 – Incorrect: Traffic studies require high temporal resolution and real-time monitoring; IRS satellites have limited revisit times and are not optimized for dynamic traffic flow analysis.